Why Frustrate?

This week, I was helping a student prepare for a chapter test on percents and their applications. He went online to take the interactive practice test and this question, and “answer”, left us scratching our heads:

If a student can mentally (correctly) calculate 56/70 as a decimal, then percent… why does he get a big ol’ red “X” for it? Sorry – just had to vent. I do not like when the textbook tries to tell my students how to think. Grrr.